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首页> 外文期刊>Electrocatalysis >Quasi-Continuous Determination of the Apparent Transfer Coefficient of Methanol Oxidation Using a Potential Modulation Technique Under Convection Conditions
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Quasi-Continuous Determination of the Apparent Transfer Coefficient of Methanol Oxidation Using a Potential Modulation Technique Under Convection Conditions

机译：对流条件下使用电位调节技术准连续测定甲醇氧化的表观传递系数

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摘要

The apparent transfer coefficient for methanol oxidation and for the oxidation of the methanol adsorption product was determined using the recently introduced ac voltammetry method [1]. To ensure fast convectional transport and avoid interference with reaction intermediates, the same dual thin-layer flow-through cell, which we typically use for differential electrochemical mass spectrometry, was used. Potential sweep and potential step experiments have been performed at polycrystalline platinum, superimposing a small sinusoidal voltage to the normal dc voltage, and the components of the ac current have been recorded. The potential dependence of the electrochemical reaction rate, described by the apparent transfer coefficient (a'), has been recorded quasi-continuously as a function of potential or time, and the corresponding Tafel slopes have been calculated. In control experiments, using adsorbed CO, values previously determined using the H cell was reproduced. This demonstrates that the method is applicable to the thin-layer cell despite of the high electrolyte resistance. Contrary to the case of the oxidation of adsorbed CO, where the transfer coefficient varies from about 1.5 at low potentials to 0.5 at high potentials, due to a change of the rate-determining step, the apparent transfer coefficient for the oxidation of methanol adsorption product is around 0.5 at all potentials, suggesting that at all potentials, the first reaction step, the adsorption of OH, is the rate-determining step (rds) and not in equilibrium. A typical a' value of 0.5 (Tafel slope of 118 mV dec-1) has been calculated at the onset potential during the potentiodynamic and potentiostatic oxidation of bulk methanol at polycrystalline platinum demonstrating that the rds is the first charge transfer with loss of one electron.
机译：使用最近引入的交流伏安法[1]确定了甲醇氧化和甲醇吸附产物氧化的表观传递系数。为了确保快速对流传输并避免对反应中间体的干扰，使用了我们通常用于差分电化学质谱分析的相同的双薄层流通池。在多晶铂上进行了电势扫描和电势阶跃实验，将一个小的正弦电压叠加到正常的直流电压上，并记录了交流电流的分量。电化学反应速率的电势依赖性，由表观传递系数（a'）描述，是作为电势或时间的函数近似连续记录的，并且已经计算出相应的Tafel斜率。在对照实验中，使用吸附的CO，可以复制先前使用H电池确定的值。这表明尽管具有高的耐电解质性，该方法也适用于薄层电池。与吸附的CO氧化的情况相反，由于速率决定步骤的变化，传递系数从低电势下的约1.5变为高电势下的0.5有所变化，甲醇吸附产物氧化的表观传递系数在所有电势下均约为0.5，这表明在所有电势下，第一步反应（OH的吸附）是决定速率的步骤（rds），而不是平衡状态。在块状甲醇在多晶铂的电位动力学和恒电位氧化过程中的起始电势下，已计算出典型的a'值为0.5（Tafel斜率为118 mV dec-1），这表明rds是第一次电荷转移，损失了一个电子。

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